Snippet.java

class Foo {
    public void showNotification(String _subText,
                                  String _bigContentTitle,
                                  String _bigText) {
  
        String channelId = "channelId";

        NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(context, channelId);

        notificationBuilder.setAutoCancel(true);

        Intent intent = new Intent(context.getApplicationContext(), YourActivity.class);

        intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TOP);

        PendingIntent pendingIntent = PendingIntent.getActivity(context, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT);

        NotificationCompat.BigTextStyle bigNotificationStyle = new NotificationCompat.BigTextStyle();
        bigNotificationStyle.bigText(_bigText);
        bigNotificationStyle.setBigContentTitle(_bigContentTitle);
        
        notificationBuilder.setContentIntent(pendingIntent);
        notificationBuilder.setSmallIcon(R.mipmap.ic_launcher);
        notificationBuilder.setSubText(_subText);

        notificationBuilder.setPriority(Notification.PRIORITY_MAX);
        notificationBuilder.setStyle(
                new NotificationCompat.BigPictureStyle()
                        .bigPicture(BitmapFactory.decodeResource(context.getResources(), R.drawable.ic_receive))
                        .setBigContentTitle(_bigContentTitle)
                        .bigLargeIcon(null)
        );

        NotificationManager notificationManager = (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            NotificationChannel channel = new NotificationChannel(channelId, channelId, NotificationManager.IMPORTANCE_HIGH);
            if (notificationManager != null) {
                notificationManager.createNotificationChannel(channel);
            }
        }
        if (notificationManager != null) {
            notificationManager.notify(0, notificationBuilder.build());
        }
    }
}